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Features/location of the pelvis (basin)
- 1. lower and smaller portion of the trunk
- 2. superiorly it is continuous with the abdomen
- 3. inferiorly it is separated from the perineum by the pelvic diaphragm (sheet of muscles)
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Functions of pelvis
- 1. Acts to transmit upper body weight to the lower limbs and provides a stable base for lower limb function
- 2. Supports and protects the pelvic viscera
- 3. Forms part of the birth canal during delivery
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What is the bony pelvis?
A ring of bone formed by the two hip bones (os coxae) anteriorly and laterally, and the sacrum and coccyx posteriorly.
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What are the 3 parts of the hip bone?
- 1. ilium
- 2. ischium
- 3. pubis
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Where do the 3 parts of the hip bone fuse?
acetabulum
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At what age do the 3 parts of the hip bone fuse?
16
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Features of the sacral canal
- -formed by the sacral vertebral foramina and is a downward continuation of the vertebral canal
- -has 4 pairs of intervertebral foramina that are continuous with the pelvic and dorsal sacral foramina
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What does the sacral canal contain?
- 1. cauda equina
- 2. filum terminale
- 3. meninges
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Where does the subarachnoid space end?
At the level of S2 vertebra
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What passes through the sacral hiatus?
- 1. filum terminale
- 2. S5 nerves
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Which side of the sacrum is concave and which is convex?
pelvic surface is concave, dorsal surface is convex
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Where are the ventral rami of S1-4 transmitted, and where are the dorsal rami of S1-4 transmitted?
- ventral rami- through the 4 pairs of pelvic sacral foramina on the pelvic surface of the sacrum.
- dorsal rami- throught the 4 pairs of dorsal sacral faramina on the dorsal surface of the sacrum.
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How many fused vertebral segments does the coccyx have?
4
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Which direction do the paired coccygeal cornua project?
dorsolaterally
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Which direction do the paired transverse processes of the coccyx project?
superiolaterally
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Description/location of pelvic inlet
- -plane bounded by the pelvic brim (linea terminalis)
- -extends along:
- 1. promontory and ala of sacrum
- 2. arcuate line of the ilium
- 3. pecten pubis
- 4. pubic crest
- 5. upper border of symphysis pubis
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The pelvic inlet divides the pelvis into what two parts?
greater pelvis (pelvis major or false pelvis) and lesser pelvis (pelvis minor or true pelvis)
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Where is the greater pelvis located?
above the pelvic inlet between the iliac bone. It is part of the abdominal cavity.
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Where is the lesser pelvis located?
below the pelvic inlet. It forms the pelvic cavity, or simply the pelvis.
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Description/location of pelvic outlet
- -diamond-shaped area extending from the symphysis pubis anteriorly to the coccyx posteriorly
- -bound on each side by:
- 1. ischiopubic ramus
- 2. ischial tuberosity
- 3. sacrotuberous ligament (ischial tuberosity -> sacrum)
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Maximum diameters of inlet and outlet in the female and significance to childbirth
- inlet- transverse diameter 13.5 cm
- outlet- A-P diameter 11 cm
- -fetal head turns 90 degrees during delivery. It faces to the side as it passes through the inlet and faces posteriorly through the outlet.
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Neutral position of the pelvis
ASIS and upper end of symphysis pubis are in same vertical plane
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Functions of the pelvic floor
- 1. support the pelvic organs and their contents (ex: bowel, bladder, uterus)
- 2. withstand any increases in pressure in the abdominopelvic cavity
- 3. provide sphincter control of the perineal openings (urethra, vagina, anus)
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General description of the perineum
-diamond shaped area between the thighs that contains the external genitalia and the anal region
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In the perineum, two triangles are formed by a line drawn between what landmarks?
the ischial tuberosities
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What two triangles make up the perineum?
urogenital triangle + anal triangle
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What separates the perineum from the pelvic cavity?
the pelvic diaphragm (levator ani and coccygeus muscles)
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What does the urogenital triangle of the perineum contain? Where is it positioned in the perineum?
external urogenital organs, positioned anteriorly
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What does the anal triangle of the perineum contain? Where is it positioned in the perineum?
end of the anal canal and anus, positioned posteriorly
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Innervates anus and external anal sphincter
inferior rectal branch of pudendal nerve (S2,3,4)
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What is the ischioanal fossa? What structures are found here?
- -a large wedge-shaped space on each side of the anus filled with fat.
- -Pudendal VAN
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External genitalia of the female
- 1. Mons pubis
- 2. Labia majora
- 3. Labia minora (forms the prepuce and frenulum of the clitoris)
- 4. Vestibule (contains openings of the urethra and vagina)
- 5. Bulbs of the vestibule (erectile tissue lying on each sideof the vaginal opening)
- 6. Clitoris (erectile tissue consisting of 2 crura and a body ending in the glans)
- 7. Greater vestibular (Bartholin's) glands (secrete mucus for vaginal lubrication)
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External genitalia of the male
- 1. Penis, consisting of 3 cylinders of erectile tissue:
- a) paired dorsal corpora cavernosa, each attached along the ischiopubic ramus by its crus
- b) unpaired ventral corpus spongiosum containing the urethra and ending in the enlarged glans. The bulb is attached to the perineal membrane.
- 2. Scrotum-a fibromuscular sac of skin containing the testes and lower parts of the spermatic cords.
- Dartos muscle- layer of smooth muscle that wrinkles the skin of the scrotum.
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The perineal branch of the pudendal nerve (S2,3,4) (that innervates the bulbospongiosus and ischiocavernosus) contains what fibers?
- somatic motor
- somatic sensory
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Features of pelvic diaphragm
- -funnel-shaped musculofibrous sheet that closes off the pelvic outlet and forms the floor of the pelvic cavity
- -consists of 2 pairs of muscles: levator ani and coccygeus
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